(i) Technical Field
The present invention relates to an optical device for holographic recording or reading and a method for controlling the same.
(ii) Related Art
A holographic recording and reading method is a method for recording or reading digital data by means of recording or reading, as a hologram, signal light in which binary digital data “0 and 1” are digitally imaged as “bright and dark”, for example. In this case, the signal light is subjected to Fourier transform by means of a lens, and a Fourier-transformed image is irradiated on an optical recording medium. Simultaneously, reference light which interferes with the signal light to generate interference fringes is also irradiated on the optical recording medium.
In such a holographic recording-and-reproduction method, an inexpensive semiconductor laser is often used as a source of recording light or reproduction light. Since output light of the semiconductor laser is weak, the recording light or reproduction light must be irradiated on the same position on an optical recording medium for a given period of time in order to enhance the accuracy of recording or reading operation.